An image sensor is a semiconductor device which converts an optical image into an electrical signal. The image sensor may be classified generally into a charge coupled device (CCD) image sensor and a complementary metal oxide semiconductor (CMOS) image sensor. The CMOS image sensor may include a photodiode for sensing illuminated light and a CMOS logic circuit for processing the detected light into an electrical signal to produce data.
As the amount of light received by the photodiode becomes larger, the image sensor has more increased photosensitivity. The photosensitivity can be improved by increasing a fill factor representing a ratio of an area of the photodiode to an entire area of the image sensor, or by changing a path of light incident on an area except the photodiode to focus the light on the photodiode. As a representative example of a light focusing technology, a micro lens (generally, a convex micro lens) may be formed on and/or over the photodiode using a highly light-transmissive material. The micro lens refracts incident light to illuminate a larger amount of light on and/or over the photodiode. In this case, light parallel to an optical axis of the micro lens is refracted by the micro lens, and a focus is formed at a specific position on the optical axis.
Further, in the CMOS image sensor, a portion of the light incident on the photodiode may be reflected by the photodiode, thereby reducing the light focusing efficiency. Accordingly, there is a disadvantage of reducing the photosensitivity of the image sensor. Thus, a reflective film may be formed above the side surface of the photodiode to reduce loss of the reflected light as disclosed in Korean Patent Application No. 10-2005-0134399, filed by the present applicant.
As illustrated in example FIG. 1, a CMOS image sensor may include photodiode 10 and reflective film 12 formed above and parallel to photodiode 10. By this configuration, it is possible to partially prevent loss of light reflected from photodiode 10. Meaning, the CMOS image sensor illustrated in example FIG. 1 may exhibit high light efficiency since light reflected from photodiode 10 is reflected by reflective film 12 to photodiode 10. However, a large amount of the reflected light is lost out of photodiode 10.